Bacillus thuringiensis var. kurstaki (Bt) and thiodicarb (Larvin) were evaluated in laboratory and field tests to determine the effect on Heliothis virescens larvae, the tobacco budworm, and the parasitoid Microplitis croceipes. Laboratory trials were conducted using Bt rates of 0, 10, 50 and 250 ppm and Larvin rates of 0, 12.5, 25, 50, 100, and 200 ppm. Field tests were conducted using Bt and Larvin, independently and in combination, at rates recommended for resistance management in Arkansas. Tobacco budworm mortality was directly related to Bt and Larvin concentration. Bt only significantly impacted tobacco budworm mortality at the highest rate of exposure in the absence of parasitization. On day 6 and 16, parasitization increased host mortality at all Bt experimental rates. Larvin exhibited a linear relationship between host mortality and increasing insecticide concentration. However, parasitization did not significantly impact host mortality until day 16. Emergence of M. croceipes was inversely related to Bt and Larvin concentration.